When it comes to sending New Year's greetings in China, the latest fashion is to say: How many electronic "red envelopes" did you receive?

For Gao Kaihong, grabbing the "red envelops" on his mobile phone was the major festive activity during the holiday.

"I sent out 36 red envelopes on lunar New Year's Eve and received 42," boasted Gao from Shijiazhuang, capital of north China's Hebei Province.

Giving "lucky money" in electronic form is a trendy spin on the Chinese tradition of giving red envelopes of money (hongbao) to children on New Year's Eve.

Over 100 million people sent gifts of money via mobile apps this year, according to Alipay, the payment system run by Alibaba.

From last Wednesday, New Year's Eve, to Saturday was the peak with a claimed 4 billion yuan (about 650 million U.S. dollars) changing hands.

Alipay's figures suggested that, unlike the tradition of elders giving red envelopes to children, over half of those sending "e-hongbao" were people in their 20s from the cities of Shanghai, Hangzhou, Beijing and Guangzhou.

Several Internet companies, including Tencent, Alibaba, Sina and Baidu, released red envelope features to grab a slice of the e-payment market for the holiday. Users must link their debit or credit cards to their accounts to send the money.

"Lucky money" payments worth one yuan were the most popular with over 19.5 million given during the holiday. E-hongbao in 88-yuan denominations were also popular and 3.2 million were exchanged during this year's festivities.

Some people interviewed by Xinhua said they "pulled an all-nighter" as they played the e-hongbao "game" on their mobile phones.

Wan Jianzhong, a folklore expert with Beijing Normal University, said the e-hongbao is a sign of traditional culture evolving in the Internet era.

"Hongbao are usually given to children by parents or older relatives, but the Internet has made the activity a universal pastime," Wan said.

With mobile Internet involved, some caution that the popularity of e-hongbao may cause some problems. Hong Tao of Beijing Technology and Business University believes it will take much time and energy to deal with the cash flow as much of the money is not withdrawn.

"Rules and regulations need to be improved regarding the e-hongbao system to guarantee its operation," Hong said.